Why can two atoms of the same element have different numbers of neutrons but must always have the same number of protons?

Answer 1

Since protons are of the same charge, they naturally repel each other within the nucleus, and since they are so close together, the repelling force is enormous. Therefore, the function of neutrons (uncharged particles) is to buffer the forces between the protons. But as atoms increase in size, there are more protons and more neutrons are needed to buffer to protons. The reason for the increase is the spherical nature of the nucleus. And the rest of the story is... that all the neutrons and protons in a nucleus, the nucleons (notice we hit you with another term - nucleon - which means a particle in the nucleus, a neutron or proton) have to undergo a magical transformation when the atomic nucleus is formed. Let's back up. The first post is exactly right. Protons, those little positively charged critters, don't like each other. It's the first law of electrostatics - opposite charges attract and like charges repel. So the protons don't like each other. What happens when any nucleus forms (by fusion or as the result of nuclear decay or by nuclear fission) is that all the nucleons (that term again meaning a proton or neutron) go to Jenny Craig and lose a bit of weight. Actually it's mass, but pretty close to the same thing. This mass is converted to binding energy or nuclear glue. That's what holds the nucleus together. Binding energy. Remember Einstein? Yeah, the genius with the freaky hair. Him. He said matter and energy are the same thing. (And the conversion factor is the square of the speed of light. Wow!) Each nucleon goes on that diet and gets slimmer. It's called mass deficit - the reduction of the mass of a nucleon made as a contribution to the creation of the binding energy necessary to hold the nucleus of an atom together. Are we good? So as heavier and heavier nuclei are formed, the number of those grumpy little protons increases to the point where we have to have progressively more and more binding energy to hold the whole thing together. And the neutrons contribute to that cause. Instant replay: heavier nuclei need progressively more binding energy to hold the nucleus together 'cause the protons (which don't like each other) are getting more grumpy, and more and more neutrons are needed to undergo mass deficit to contribute to increased binding energy to make the whole thing stay together. It's clear what you're thinking. You're thinking, "Hey, there must be a point where we just can't get enough binding energy to glue a super heavy nucleus together." You're right. Absolutely correct.

Answer 2

The answer lies in the reason that a nucleus sticks together. Recall that the nucleus of an atom contains protons and neutrons (except most hydrogen, which is hydrogen-1). And protons don't like each other. They repel each other; they don't want to get with the program. The protons are trying to push the atomic nucleus apart, so what holds the nucleus together?

Atoms are created by fusion, and in fusion, all the nucleons (the particles that will be making up the nucleus, those protons and neutrons) will be giving up a bit of their mass. This happens in the fusion process, and that mass will be converted into binding energy (or nuclear glue) to hold the whole thing together. At higher mass numbers, the energy needed to bind all the protons together rises quickly, and more neutrons are needed to contribute some of their mass to create the extra binding energy. That's why the approximately one-to-one ratio of protons to neutrons only holds true at low atomic numbers. Go on up the Periodic Table of elements, and more and more neutrons are needed to make more and more binding energy.

You probably figured out that at the very high atomic numbers, the atomic nucleus simply cannot be kept together by the binding energy. There just can't be enough created in any fusion reaction. Heavier and heavier elements cannot be made and kept together. And you would be absolutely correct thinking that, because that's the way it is.

Answer 3

It doesn't necessarily. To be neutral an atom must have the same number of protons and electrons. This is because a proton has a 1+ charge and an electron has a 1- charge. When they are present in equal numbers the charges cancel out to zero.

Neutrons, being neutral, have no affect on the charge of an atom. The heavier elements have more neutrons than protons, but still form neutral atoms.

Answer 4

Atoms do not always have the same number of neutrons and protons. The ratio of neutrons and protons is determined by whether or not that ratio produces a stable atom. If there are too many or not enough neutrons, the atom may not be stable. It will either not form, or it will be unstable and radioactive if it does not have the right amount of neutrons.

Answer 5

We know the nucleus of an atom is composed of protons and neutrons. The protons are trying to push each other away, but the residual strong force, which can also be called nuclear binding energy or nuclear glue, holds the nucleus together. When an atomic nucleus is first made, the protons and neutrons in it all undergo what is called mass deficit to create the binding energy necessary to hold the nucleus together. A bit of their mass is converted into this nuclear binding energy. As we move up the periodic table and atomic nuclei get larger, the repulsive forces created by all those positively charged protons gets really large. And the nucleus needs increasing binding energy to hold all the protons together. The "extra" or increased binding energy needed to stabilize the nucleus come from neutrons. At the lower end of the periodic table, there is an approximately one-to-one ratio of neutrons to protons. But as we move up the periodic table, the ratio increases gradually as the neutrons begin to outnumber the protons. This explains why as we move up the periodic table, atoms have more neutrons than protons.

Answer 6

The chemical properties of any given atom depend upon the number of protons and do not depend upon the number of neutrons in the nucleus. That is because the protons are electrically charged (each proton has a charge of +1) and neutrons have no charge. Because of the positive charge of the protons, the atomic nucleus is able to attract negatively charged electrons to orbit (or surround) the nucleus. It is the electrons, and their particular arrangement, which then give atoms their chemical characteristics.

Answer 7

That isn't true.

A neutral (non-ion) atom will have equal numbers of electrons and protons, giving the atom a net charge of zero.

Neutrons are required to stabilise the nucleus in all elements with 2 or more protons. Often the neutron count is very similar to the count of protons. Atomic nuclei may be stabilised by different numbers of neutrons.

For example, a neutral hydrogen-1 atom has zero neutrons, but one electron.

Mercury, Hg has an atomic number of 80, therfore has 8-0 electrons. It has 7 stable isotopes which are all presnt in naturally occuring mercury with neutron counts of 116 and above.

This table is taken from wikipedia. the % are those in naturally occuring mercury.

196Hg

0.15%

196Hg is stable with 116 neutrons

198Hg

9.97%

198Hg is stable with 118 neutrons

199Hg

16.87%

199Hg is stable with 119 neutrons

200Hg

23.1%

200Hg is stable with 120 neutrons

201Hg

13.18%

201Hg is stable with 121 neutrons

202Hg

29.86%

202Hg is stable with 122 neutrons

204Hg

6.87%

204Hg is stable with 124 neutrons

Answer 8

Atoms do not always contain the same number of electrons and protons, although this state is common. When an atom has an equal number of electrons and protons, it has an equal number of negative electric charges (the electrons) and positive electric charges (the protons). The total electric charge of the atom is therefore zero and the atom is said to be neutral. In contrast, when an atom looses or gains an electron (or the rarer case of loosing or gaining a proton, which requires a nuclear reaction), the total charges adds up to something other than zero. The atom is then said to be electrically charged, or "ionized". There is a major difference between the neutral state and the ionized state. In the neutral state, an atom has little electromagnetic attraction to other atoms. Note that the electric field of a neutral atom is weak, but is not exactly zero because the atom is not a point particle. If another atom gets close enough to the atom, it may end up closer to a negatively charged part of the atom than the positively charged part. Because the electric field dies off with distant, it feels the field from the negatively charged part more strongly than the field from the positively charged part. This non-zero electric field then deforms the electron cloud shapes in both atoms so that electric dipoles are formed, which are then attracted together. When perfectly neutral atoms get close enough, they can still stick together electrically in this way. This form of the electromagnetic force is called the "Van der Walls force" or the "London dispersion force", and is very weak.

Answer 9

Atoms are made of protons, neutrons and electrons (sub atomic particles). Therefore, a proton must be smaller than an atom.